1. WGG Coal Retirement Case Transmission Repurposed for Renewables

2. 2 2022 PC6 – WGG Coal Retirement Case (transmission repurposed) Purpose: to attempt to maximize the delivery of renewable energy and minimize the construction of new transmission while also trying to achieve a targeted reduction in carbon emissions.

3. 3 2022 PC6 – WGG Coal Retirement Case (transmission repurposed) Central Questions 1) How much transmission capacity can be made available by retiring 5400 MW coal resources? 2) What is the amount of new renewable resource capacity that could feasibly utilize this freed up transmission capacity? 3) What is the resulting utilization of the transmission facilities when re-purposed to transport renewables? 4) What is the resulting reduction in WECC-wide carbon emissions produced by this re-purposing?

4. 4 2022 PC6 – WGG Coal Retirement Case (transmission repurposed) Assumptions Loads – decreased to reflect the assumption that “all cost-effective EE potential” is achieved throughout the West (PC4 assumption) Transmission System – Path rating reductions Generation – o DG resources increased based on ‘interconnection potential’ of distributed PV and ‘technical potential’ of distributed CHP as estimated by E3 (link to E3 report)link o RPS resources adjusted for lower loads due to EE and behind-the-meter DG, and for increased PV DG o DSM increased based on LBNL analysis of demand response potential estimated using an updated FERC DR Potential Estimates model o Retired 25% of WECC coal fleet (5400 MW) o Added renewables to repurpose transmission (~4400 MW)

5. Study Execution Build and run study in steps… 1)Perform EE load adjustments; 2)Add DG resources, adjust RPS 3)Add DR and “tune” 4)Retire coal plants 5)Check for reliability impact due to retirement 6)Run case 7)Quantify new renewable generation that could be accessed/delivered using transmission capacity previously utilized by retired coal 8)Add renewables from (7) 9)Run final study Complete PC4 Complete PC6

6. WGG Coal Retirement Case LoadsGenerationTransmission PC4 Assumptions: Low load PC4 Assumptions: DG + DR Path rating reductions Retire Coal (5400 MW) Add Renewables (4400 MW)

7. WGG Coal Retirement Case LoadsGenerationTransmission PC4 Assumptions: Low load PC4 Assumptions: DG + DR Path rating reductions Retire Coal (5400 MW) Add Renewables (4400 MW)

8. Summary of Aggressive EE Load Adjustments

9. WGG Coal Retirement Case LoadsGenerationTransmission PC4 Assumptions: Low load PC4 Assumptions: DG + DR Path rating reductions Retire Coal (5400 MW) Add Renewables (4400 MW)

10. 10 2022 Incremental Distributed CHP in PC1 and PC4 – Big Picture WECC total ~ 9,900 MW

11. DR Capacity chart

12. WGG Coal Retirement Case LoadsGenerationTransmission PC4 Assumptions: Low load PC4 Assumptions: DG + DR Path rating reductions Retire Coal (5400 MW) Add Renewables (4400 MW)

13. Coal Retirements Selected ArizonaColoradoMontanaNevada New Mexico UtahWyoming Apache 2Mrtn Drake 5Colstrip 1Valmy 1Four Crnrs 4Carbon 1Dave Johnston 1 Apache 3Mrtn Drake 6Colstrip 2San Juan 4Carbon 2Dave Johnston 2 Cholla 1Mrtn Drake 7Corette 1Kennecott 1Dave Johnston 3 Cholla 3Nucla 1Kennecott 2Naughton 1 Irvington 4Nucla 2Kennecott 3Naughton 2 Nucla 3Sunnyside 1Osage 1 Nucla 4Osage 2 W.N. Clark 1Osage 3 W.N. Clark 2Wygen 3 Wyodak 1 Total MW (retired capacity, total of 5366 MW) 83841682426512774501297

14. Coal Retirements Selected 25% of WECC coal fleet –3250 MW retired prior to 2022 in the Common Case –5370 MW retired based on WGG’s economic analysis

15. WGG Coal Retirement Case LoadsGenerationTransmission PC4 Assumptions: Low load PC4 Assumptions: DG + DR Path rating reductions Retire Coal (5400 MW) Add Renewables (4400 MW)

16. 16 Incomplete information provided by the Technical Studies Subcommittee (TSS) o Retirement – Colstrip 1 and 2  Path 8 Montana-Northwest derated to 1600 MW o Retirement – Nucla 1-4  TOT 2 derated to 690 MW minus output of Nucla 1-4 (total max cap of 115 MW) Path rating catalog reviewed to identify additional path rating impacts; no conclusive information found Path Rating Impacts of Selected Retirements

17. WGG Coal Retirement Case LoadsGenerationTransmission PC4 Assumptions: Low load PC4 Assumptions: DG + DR Path rating reductions Retire Coal (5400 MW) Add Renewables (4400 MW)

18. 18 Add incremental renewable resources to WREZ zones closest to the retired coal plants, attempting to take advantage of any freed-up transmission capacity Used capacity values from various resources to recalculate PRM and decide how many new CTs to add Adding Incremental Renewables

19. Added Renewables State GeothermalSolar CSPSolar PVWind Total MWGWhMWGWhMWGWhMWGWhMWGWh Arizona11534341410645291407 Colorado331874331874 Montana90628509062850 Nevada26520682652068 New Mexico7352073385859684233418045266 Utah450991450991 Wyoming1427555114275551 Total265206895524168351850376212673571219007

20. 20 Coal Retirements vs. New Renewables & CTs - Wyoming/Montana Area Coal Plant Retirement WREZ Hub centroid, approximate location of incremental renewables WECC Path Cut Plane Incremental wind resource Incremental CTs 906 MW 1,012 MW 415 MW 450 MW 380 MW 370 MW

21. 21 Wyoming: o Coal retired – 1,297 MW o Incremental wind added – 1,427 MW o Incremental CTs added – 1,200 MW Montana: o Coal retired – 824 MW o Incremental wind added – 906 MW o Incremental CTs added – 0 MW Wyoming/Montana Area Summary

22. 22 Coal Retirements vs. New Renewables & CTs – Colorado/New Mexico Area Coal Plant Retirement WREZ Hub centroid, approximate location of incremental renewables WECC Path Cut Plane Incremental wind resource Incremental CTs 330 MW 684 MW Incremental solar resource 770 MW 200 MW

23. 23 Colorado: o Coal retired – 416 MW o Incremental wind added – 330 MW o Incremental CTs added – 0 MW New Mexico: o Coal retired – 1,277 MW o Incremental wind added – 684 MW o Incremental solar added – 770 MW o Incremental CTs added – 200 MW Colorado/New Mexico Area Summary

24. 24 Coal Retirements vs. New Renewables & CTs – Nevada/Utah/Arizona Area Coal Plant Retirement WREZ Hub centroid, approximate location of incremental renewables WECC Path Cut Plane Incremental wind resource Incremental CTs Incremental solar resource 300 MW Incremental geothermal resource 265 MW 450 MW 414 MW 115 MW 350 MW

25. 25 Nevada: o Coal retired – 265 MW o Incremental geothermal added – 265 MW o Incremental CTs added – 0 MW Utah: o Coal retired – 450 MW o Incremental solar added – 450 MW o Incremental CTs added – 300 MW Arizona: o Coal retired – 841 MW o Incremental wind added – 414 MW o Incremental solar added – 465 MW o Incremental CTs added – 0 MW Nevada/Utah/Arizona Area Summary

26. 26 Coal retirements selected for this study are based solely on an economic analysis performed by the Synapse modeling tool created for WGG. Tool’s input was public information available at the time of the tool’s creation. No capital cost analysis was completed as part of this case primarily due to the unavailability of information needed to assess costs associated with plant retirements. Study Caveats to be Noted

27. 27 A full assessment of the reliability impacts of the modeled coal retirements cannot be completed as part of this study (at this time). Many possible combinations of renewable resources could be analyzed as part of this study, but only a single selection of incremental renewable resources was selected for this case. Caveats, cont.

28. 28 The net transmission impact, production cost impact, generation dispatch impact, and carbon impact of retiring approximately 5400 MW of coal and replacing it with ~5400 MW of renewable resources (plus CTs needed for load/gen balance) What Will This Case Tell Us?

29. 29 The maximum capacity of renewable resources that could replace the retired coal without impacting the transmission system The reliability impact of retiring 5400 MW of coal around the Western Interconnection The cost of retiring 5400 MW of coal and replacing it with an equivalent capacity of renewables What Will This Case Not Tell Us?

30. WGG Coal Retirement Case Generation Impact

31. Load is 10% less! and change in multiple resource assumptions ? ?

32. Too many variables!

33. Same load…isolated variables Retire Coal (5400 MW) Add Renewables (4400 MW)

34. Retire Coal (5400 MW) Add Renewables (4400 MW) Energy

35. WGG Coal Retirement Case Production Cost and CO2 Impact

36. Production Cost Summary Category 2022 PC1 Common Case 2022 PC6 Carbon ReductionDifferenceDiff % Dump Energy397,1041,519,3001,122,196282.595% Emergency Energy2,6761,372(1,305)-48.742% CO 2 Emissions (MMetricTons)359282(78)-21.627% CO 2 Adder ($/metric ton)0.000 Variable Production Cost (thermal units excl DSM) CO 2 Adder (Total M$)0000.000% Other Variable Costs (M$)14,85111,963(2,888)-19.446% Total Var. Prod. Cost (M$)14,85111,963(2,888)-19.446%

37. Production Cost Summary Category 2022 PC4 High EE-DG-DR 2022 PC6 Carbon ReductionDifferenceDiff % Dump Energy1,515,2661,519,3004,0340.266% Emergency Energy1,372 00.000% CO 2 Emissions (MMetricTons)310282(29)-9.207% CO 2 Adder ($/metric ton)0.000 Variable Production Cost (thermal units excl DSM) CO 2 Adder (Total M$)0000.000% Other Variable Costs (M$)11,90211,963610.514% Total Var. Prod. Cost (M$)11,90211,963610.514%

38. Summary of Production Cost and CO2 Production Cost: Savings of 20% from the Common Case is due to the PC4 assumptions, not the Coal Retirement Assumptions CO2: About half of the 20% reduction in CO2 emissions from the Common Case is due to the coal retirements and added renewables. The other half can be credited to PC4 assumptions.

39. WGG Coal Retirement Case Transmission Impact

40. De-rated

43. 2022 Common Case Results Most Heavily Utilized Paths Passed 3 Passed 2 Passed 1 P45 P26 P8 P3 P29 P47 P60 P27 P1 P11/10

44. Summary Transmission impact → relatively small? Production cost impact → small Generation dispatch impact → significant Carbon impact → significant